chore: automate more of the release process

[maxrjones]

This PR aims to simplify our release process via more automation:

• Add a github workflow that will open a PR with the consolidated changelog entry
• Add a github workflow that will run relevant tests from the xarray/numcodecs repos
• Update the release checklist to remove extra items and focus on the typical process of releasing from main

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/user-guide/*.md
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[d-v-b]

comparison between this approach and https://github.com/googleapis/release-please or similar tools?

[maxrjones]

comparison between this approach and googleapis/release-please or similar tools?

Towncrier and release-please serve somewhat similar purposes, but release-please has a broader scope handling releases in addition to changelogs. release-please relies on conventional commits whereas towncrier relies on manual fragments.

This PR focuses on automating the system we already adopt (towncrier) rather than proposing a new system (e.g., release-please). This PR includes automating downstream tests, which are not solved by tools like towncrier or release please.

[d-v-b]

This PR includes automating downstream tests, which are not solved by tools like towncrier or release please.

I didn't see how that is wired up -- isn't the downstream testing job just on workflow dispatch?

[maxrjones]

This PR includes automating downstream tests, which are not solved by tools like towncrier or release please.

I didn't see how that is wired up -- isn't the downstream testing job just on workflow dispatch?

58f74a6 (this PR) added a trigger for the downstream run based on a label, which is automatically added to the towncrier PR. the towncrier PR is opened via workflow dispatch.